The present invention relates to an image reading apparatus for reading an image on an original document, for use in facsimile equipment, a digital copier, a scanner or the like.
Recent advancements in computerized work stations and personal computers have led to devices that can perform advanced processing functions including image editing, electronic filing and character input by OCR at high speeds. In order to provide digitized images to the work stations and personal computers, image scanners capable of easily entering original images at high resolutions and increased speeds are increasing being required to match the trend in workstation and personal computer advances.
A schematic structure of a conventional image scanning or reading apparatus is shown in FIG. 10. In FIG. 10, reference numeral 1 is an image reading apparatus, 2 is an original document, 3 is a glass platen, 4 is a carriage, 5 is a drive motor, 6 is a drive wire, 7 is a light source, 8 is a reflector, 9 is a lens, and 10 is a CCD line sensor.
In the conventional image reading apparatus shown in FIG. 10, two scanning directions are used when reading the image, that is, a main scanning direction of scanning in the pixel line direction of the CCD line sensor 10, and a subsidiary scanning direction along the movement of the carriage 4.
When the CCD line sensor 10 reads the document 2 during an image reading operation, a reading trace as shown in FIG. 11 is generated. The reading trace in the main scanning direction is only the portion of one pixel of the CCD line sensor 10 shown in the scan area S1 at the main scanning side in FIG. 11.
In contrast, the reading trace S2 in the subsidiary scanning direction is a range of two rows of the CCD line sensor 10 owing to the accumulation time of the CCD line sensor 10. As a result, the signal data of the CCD line sensor 10 entered in the processing circuit becomes the average of the signals from two rows of the sensor.
Accordingly, when the original image shown in FIG. 12A is read by the conventional method, the resolution deteriorates in the subsidiary scanning direction, and the image is blurry, as shown in FIG. 12B. Such image blurring is called the move average effect. Thus, in the image reading process of the conventional image reading apparatus, there are problems of lowering of resolution in the subsidiary scanning direction.
It is hence the objects of the present invention to provide an image reading apparatus capable of decreasing the move average effect in the subsidiary scanning direction and preventing lowering of resolution in the subsidiary scanning direction, and to provide a processing method of image signal.
To solve the above problems, the image reading apparatus of the invention comprises
a) a light source for illuminating an original document,
b) an optical system for focusing a reflected light or transmitted light from the original document,
c) a carriage capable of moving at least the light source relatively to the original document in the subsidiary scanning direction,
d) a photoelectric converter of a line form for converting the focused original image into an electric signal in every pixel for one line,
e) and an electric circuit for controlling the entire apparatus.
The operation of the image reading apparatus can be changed between an ordinary image reading mode and a subsidiary scanning fine reading mode according to the selection of the users of the apparatus. In the ordinary image reading mode, the moving speed of the movable carriage predetermined for the resolution in the subsidiary scanning direction is determined by a central processing unit. And, also, in the subsidiary scanning fine reading mode, the moving speed of the movable carriage can be set to 1/n of the moving speed of the carriage in the ordinary image reading mode according to the selection of the users of the apparatus. In this case the reading signal data from the photoelectric converter of a line form is taken into the signal processing circuit in every 1/n times of the number of times of incorporating the signal data in the ordinary image reading mode.
In another feature of the invention, the user of the image reading apparatus of the present invention is capable of setting the value of above-mentioned n arbitrarily. By controlling the value of n, the user can control the degree of fineness they need, and hence are capable of preventing deterioration of resolution in the subsidiary scanning direction by increasing the value of n.
According to the constitution of the present invention, in an image input into the image reading apparatus, the lowering of resolution in the subsidiary scanning direction can be prevented by decreasing the move average effect in the subsidiary scanning direction.